Conventionally, in the field of semiconductor device fabrication, plasma processes are widely used. Plasma processing includes, for example, plasma etching and plasma chemical vapor deposition (CVD). Plasma etching is used to form a fine pattern of the semiconductor device and is an important basic technology together with lithography. In large scale integration (LSI) devices, the variations in the film or types of films as well as finer pattern requirements, have placed increasing demands upon microfabrication performance and uniform control technology, particularly for a large diameter wafer of, e.g., 300 mm or more in the plasma etching.
Conventionally, parallel plate, electron cyclotron resonance (ECR), inductive coupled plasma (ICP) and the like have been developed as plasma sources for plasma etching. For example, Japanese Patent Laid-open Publication No. 2008-47687 discloses a plasma etching apparatus using a parallel plate as a plasma source. In this parallel plate type plasma etching apparatus, a pair of an upper electrode and a lower electrode parallel to each other is disposed in a processing chamber. While a high frequency power is applied to the lower electrode, etching is performed on a substrate mounted on the lower electrode.
In order to improve the uniformity in the surface of the substrate to be etched, the upper electrode is divided into a central portion for supplying a processing gas to the center of the substrate, and a peripheral portion for supplying a processing gas to the periphery of the substrate. Then, a common processing gas is supplied to the substrate from the central portion and the peripheral portion of the upper electrode, and an additive gas is added to the common gas in the peripheral portion. By adding the additive gas, it is possible to improve the in-surface non-uniformity of etching caused by the fact that the central portion of the substrate is hardly exhausted compared to the peripheral portion.
In recent years, there has been developed a plasma etching apparatus using a radial line slot antenna as a plasma source (see, e.g., Japanese Patent Laid-open Publication No. 2010-118549). In the plasma etching apparatus using the radial line slot antenna, a slot antenna having a plurality of slots is installed on a dielectric window of a processing chamber. A microwave emitted from the slots of the slot antenna is introduced into a processing space of the processing chamber through the dielectric window made of a dielectric material. The processing gas is converted into a plasma by the energy of the microwave.
The microwave plasma generated by the radial line slot antenna is characterized in that a plasma having a relatively high electron temperature of several eV is generated immediately below the dielectric window (referred to as plasma excitation region), and diffuses and becomes a plasma having a low electron temperature of about 1 to 2 eV immediately above the substrate located at a position lower at least 100 mm than the dielectric window (referred to as plasma diffusion region). That is, it is characterized in that the change in the electron temperature of the plasma occurs as a function of distance from the dielectric window.
In the radial line slot antenna type plasma etching apparatus, the etching gas is supplied to the low electron temperature region, and a dissociation control of the etching gas (control of the generation amount of etching species in the plasma) is performed, thereby controlling the etching reaction (chemical reaction of the substrate surface by etching species). Accordingly, high precision of etching is promoted and damage to the substrate is greatly reduced. For example, it is possible to suppress the damage, such as a recess to the substrate, while manufacturing a device according to design dimensions in etching or the like in the step of forming a spacer.
In recent years, with variations in the films and the use of various types of films, or the improvement of the microfabrication performance of semiconductor devices, both various dissociation controls of the etching gas and control of in-surface uniformity of the substrate are needed.
However, in the parallel plate type plasma etching apparatus described in Japanese Patent Laid-open Publication No. 2008-47687, a plasma generated between upper and lower electrodes that are separated by a short distance of 40 mm or less is used, and the electron temperature of the plasma is kept high until it reaches the lower electrode from the upper electrode. Further, both the common gas and the additive gas are introduced into the upper electrode. Accordingly, there is a problem in that the dissociation of the common gas and the additive gas cannot be controlled in various levels.
In the etching apparatus using the radial line slot antenna disclosed in Japanese Patent Laid-open Publication No. 2010-118549, it is difficult to make constant the etching shape or the etching rate in the surface of the substrate, and it has become a challenge to uniformly perform the etching process in the surface of the substrate.
In view of the above, the present invention provides a plasma processing apparatus and method capable of controlling the dissociation state of a processing gas in various levels and also controlling the in-surface uniformity of the substrate processing.